1. Field of the Invention:
This invention relates to a backlighting detecting device for performing detection of the backlighting condition of a field of view.
2. Description of the Related Art:
The necessity of detecting the backlighting condition of a field of view arises in a situation where the luminance difference between a main subject portion and a background portion of a scene is so great that it is difficult to derive a proper exposure value for both the subject and the background. In more detail, the scene is such as that if the exposure is adjusted for the subject by using the spot light measuring mode or the like, a considerably large over-exposure will result in the portion of the background, because it is of high luminance. The use of the center-weighted average light measurement in view of a proper exposure over the entire area of the picture frame, on the other hand, will result in considerable under-exposure of the portion of the subject, because it is relatively low in luminance. Upon detecting such a backlighting condition, automatic fill-in flash may be fired. If so, even in such a scene, a good photograph can be taken of a portion of the subject saved from under-exposure, while nevertheless properly exposing a to portion of the background.
There has been a previous proposal for dividing the field of view into a plurality of areas, so that light measurement is performed by each one of the areas, and the light values obtained therefrom then being computed to detect whether the given photographic situation is in the backlighting condition.
For example, a light sensor responsive to the entire field of view and another light sensor responsive to a portion of the field of view are used in combination with a light measuring circuit, so that backlighting is detected by finding the difference between the two light values, as, for example, in Japanese Patent Publication No. Sho 47-34343. Another type a disclosed in Japanese Laid-Open Patent Application No. Sho 57-29036 is that the field of view is divided into a plurality of areas in which light measurement is performed, and the largest and smallest values are used in computation to detect the backlighting condition.
However, the prior known devices may encounter many situations where false backlighting detection results may be produced. For example, in the above-described Japanese Patent Publication No. Sho 47-34343, if the subject of principal interest is much smaller than the area of that sensor of partial responsibility, backlighting is impossible to detect.
Also, if the field of view surrounding the subject consists of a mixture of objects of high luminance and objects of lesser luminance (for example, in the landscape, a clear sky and the sun as the background and a shadowed earth as the foreground) then the light sensor for the integral field of view does not produce an output representing a very high light value. Even with a backlighting scene, therefore, some cases may be encountered where the backlighting condition is not detected as it stands.
The other of the above-described documents, Japanese Laid-Open Patent Application No. Sho 57-29036, does not take into consideration the discrimination between the subject and the background . In landscape photography, particularly when the scene consists of a mixture of dark parts, and, luminous parts a problem often arises that the backlighting detecting device detects a backlighting condition.
In U.S. Pat. No. 4,782,357, an attempt has been made to overcome this problem of detecting true backlighting conditions by utilizing a special light measuring pattern which has become the premise of the present invention.
A goal of the present invention is to assure detection of true backlighting accurately and reliably particularly in photographic situations where the field surrounding the subject consists of a mixture of luminous areas and dark areas.